化学学报 ›› 2020, Vol. 78 ›› Issue (12): 1426-1433.DOI: 10.6023/A20070330 上一篇    下一篇

研究论文

磷酸锂原位包覆富锂锰基锂离子电池正极材料

刘九鼎a, 张宇栋a, 刘俊祥a, 李金翰a, 邱晓光a, 程方益a,b,c   

  1. a 南开大学化学学院 先进能源材料化学教育部重点实验室 天津 300071;
    b 南开大学 新能源转化与存储交叉科学中心 天津 300071;
    c 南开大学 高效储能教育部工程研究中心 天津 300071
  • 投稿日期:2020-07-28 发布日期:2020-10-12
  • 通讯作者: 程方益 E-mail:fycheng@nankai.edu.cn
  • 基金资助:
    项目受科技部重点研发计划(No.2016YFA0202503)和国家自然科学基金(Nos.21925503,21835004)资助.

In-situ Li3PO4 Coating of Li-Rich Mn-Based Cathode Materials for Lithium-ion Batteries

Liu Jiudinga, Zhang Yudonga, Liu Junxianga, Li Jinhana, Qiu Xiaoguanga, Cheng Fangyia,b,c   

  1. a Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry, Nankai University, Tianjin 300071, China;
    b Renewable Energy Conversion and Storage Center, Nankai University, Tianjin 300071, China;
    c Engineering Research Center of High-efficiency Energy Storage (Ministry of Education), Nankai University, Tianjin 300071, China
  • Received:2020-07-28 Published:2020-10-12
  • Supported by:
    Project supported by the Ministry of Science and Technology of the People's Republic of China (No. 2016YFA0202503) and the National Natural Science Foundation of China (Nos. 21925503, 21835004).

本工作通过“碳酸盐共沉淀-沉淀转化-固相反应”方法,实现磷酸锂原位包覆和改性富锂锰基锂离子电池正极材料Li1.2Mn0.54Co0.13Ni0.13O2,研究了磷酸锂包覆层的形成过程及其对电化学性能的影响.结果显示,碳酸盐前驱体经沉淀转化反应原位形成磷酸镍包覆层,与锂源混合煅烧,最终转化为厚度小于30 nm的磷酸锂包覆层.该材料组装的半电池在125 mAh·g-1电流密度下循环175圈后容量达191.1 mAh·g-1,容量保持率为81.8%,平均每圈电压衰减仅为1.09 mV.磷酸锂包覆层缓解了材料表面与电解液之间的副反应,抑制了不可逆相变和过渡金属溶出,同时磷酸锂作为锂离子导体促进锂离子传输.本工作表明沉淀转化法原位包覆磷酸锂是提升富锂锰基正极材料性能的有效途径.

关键词: 富锂锰基正极材料, 锂离子电池, 磷酸锂, 原位包覆, 沉淀转化

Lithium-rich manganese-based oxides (LRMO) are promising cathode materials to build next generation lithium-ion batteries because of high capacity and low cost. However, the severe capacity fade and voltage decay, which originate from surface oxygen loss, side reactions and irreversible phase transformation, restrict their practical application. Proposed approaches to address these issues include electrolyte modification, synthesis condition optimization, tuning elemental composition, bulk doping and surface coating. Surface coating has been proved to be an effective method to stabilize the interface between LRMO and electrolyte. Herein, we report a facile approach to synthesize Li3PO4-coated LRMO (LRMO@LPO) by in-situ carbonate-phosphate precipitate conversion reaction. The formation of Li3PO4 layer and its contribution to enhanced electrochemical performance are investigated in detail. Transmission electron microscopy (TEM) reveals that the surface of carbonate precursor converts to Ni3(PO4)2 after reacting with Na2HPO4 solution, which finally transforms to Li3PO4 coating layer with thickness below 30 nm during calcination process. Quinoline phosphomolybdate gravimetric method gives the optimal Li3PO4 coating content of 0.56%. The modified LRMO@LPO sample exhibits improved cycling stability (191.1 mAh·g-1 after 175 cycles at 0.5C between 2.0~4.8 V and 81.8% capacity retention) and suppressed voltage decay (1.09 mV per cycle), compared with bare LRMO material (72.9% capacity retention, 1.78 mV per cycle). The electrodes are studied by galvanostatic intermittent titration technique, electrochemical impedance spectroscopy, TEM and inductively coupled plasma atomic emission spectrometry. The results suggest efficient mitigation of phase transformation and dissolution of transition metal in LRMO@LPO. As a coating material with lithium-ion conductivity, Li3PO4 not only acts as a physical barrier to inhibit side reaction between the electrolyte and LRMO, but also promotes lithium ion transport at the surface region of cathode. The in-situ surface modification approach simplifies the traditional post coating process, and may provide new insight to build stable and low cost Li-rich cathode for lithium-ion batteries.

Key words: Li-rich Mn-based cathode materials, lithium ion battery, Li3PO4, in-situ coating, precipitate conversion